DETROIT -- General Motors' next-generation full-sized pickups offer "evolutionary" exterior styling changes but significant engine and interior improvements, in a bid by GM to cater to buyers who use their trucks to make a living.

GM officials touted the improved power, refinement and functionality of the redesigned 2014 Chevrolet Silverado and GMC Sierra pickups -- the company's top-selling model line and biggest profit source -- today at a film studio in suburban Detroit where the trucks were introduced.

While fuel efficiency should improve for each of three new engine choices, final mpg estimates will be released later, it's clear that GM believes its pickup customers value torque and toughness more than mpg.

"Our customers rely on their trucks to meet the day-to-day challenges of earning a living, running a business," Mark Reuss, president of GM North America, said in a statement. "Chevrolet is committed to giving truck customers the most refined, best-engineered pickups in the market."

GM's pickup strategy diverges from that of rival Ford Motor Co., which has enjoyed surprising success by touting the fuel efficiency of its six-cylinder EcoBoost offering on the top-selling F-150 pickup. GM won't chase Ford with its own turbocharged six-banger.

Instead, GM is relying on a family of three engines, versions of its next generation of small-block engines, to deliver better power and competitive fuel efficiency. It will no longer offer a hybrid truck because of low sales volumes, a spokesman said.

The new engines are "100 percent truck, specifically designed for the way customers use trucks in the real world," Jordan Lee, chief engineer for the small-block engine, said in a statement.

GM wants to keep its full-sized pickups as workhorses while giving fuel-conscious buyers another alternative, Reuss has said.

That's why, unlike Ford and Chrysler Group, GM decided to continue marketing the mid-sized Chevy Colorado and GMC Canyon pickups. Redesigned versions of those trucks are expected to go on sale by late 2013 or early 2014.

GM has much riding on the strategy. The Silverado and Sierra are the company's most lucrative vehicle lines -- bringing in around $12,000 in profit per unit, analysts estimate -- and together are GM's highest-volume U.S. products.

GM execs hope the summer launch of the trucks, delayed by the company's 2009 bankruptcy, will help reverse a steady slide in its share of the full-sized pickup market. It has declined from 42.2 percent in 2002 to 35.7 percent this year, its lowest level during that decade, according to the Automotive News Data Center.

The Silverado has been the perennial No. 2-selling vehicle in the United States, behind the Ford F series pickup. But it has dropped to No. 3 this year behind the F series and Toyota Camry.

Since the fall 2006 launch of the current Silverado and Sierra, GM has offered few enhancements. Over the past few years, the trucks have become long in the tooth relative to rivals and now are the oldest full-sized pickups on the market.

Ford and Chrysler have made more frequent and substantial improvements to the F series and Ram 1500, and gained share in the segment. Ford added EcoBoost and its MyFord Touch infotainment and control system to the F-150 in the middle of its life cycle, for instance.

GM said today it will begin producing 2014 Silverado and Sierra crew cabs, which account for more than 60 percent of its current truck volume, in the second quarter of 2013. Other cab styles will go into production later in the year, GM said.

The timing could be good for GM. Analysts and GM execs expect the nascent strength in the U.S. housing market over the next few years will aid pickup sales.

The Silverado's exterior styling "can be described as evolutionary, but the updates to the interior are dramatic," the pickup's design director, Helen Emsley, said in a statement.

The Silverado and Sierra sport taller profiles than their predecessors. Each has a more muscular look, with domed hood and more-sculpted body sides.

A wider, one-piece bumper wraps around the front of the trucks, from fender to fender, giving them a wider stance. Both feature bolder, squared fender flares; the Silverado's flares are wider, while the Sierra's are more creased.

The trucks are more aerodynamic, with doors that are inlaid to fit into the recesses in the side of the body, rather than wrapping over the roofline. The doors also are more tightly sealed to reduce wind noise.

GM used more high-strength steel, including some hydroformed steel, in the truck cab, main rails and cross members to reduce mass. The hoods are aluminum, saving about 17 pounds compared with the steel hoods on current models.

Isolating the cabin

The pickups will offer a more comfortable ride, quieter cabin and better handling, GM says. A third hydraulic body mount was added to better isolate the cab from the frame to reduce noise and vibration, providing "a solid, refined feel with no loss in traditional truck capability," GM says.

In the front suspension, the use of lighter, stiffer aluminum control arms on some models, along with stiffer front springs, should provide more confident handling, GM says.

Electronic power steering was added to improve feel and save fuel because it doesn't require an engine-driven pump. For the brakes, GM will use its hardened, rust-resistant Duralife rotors, which can double the life of the rotors.

Other new features include a step on the corner of the rear bumper that, combined with new handholds in the box rail protectors, will make it easier to climb up into the bed. GM says an internal torsion bar in the tailgate will also make it easier to raise and lower.

LED lamps are installed under the bed rails. GM has added a 6-foot-6-inch box to crew cab models to join the 5-foot-8-inch box that's already offered.

GM also is borrowing several safety features recently introduced on Cadillac nameplates and other models. They include optional lane-departure warning and forward collision alert, which uses a camera to monitor the distance from another vehicle in front of the truck and warn the driver of an impending rear-end crash.

The Sierra will offer a new GM technology, first used on the recently launched Cadillac XTS, that alerts the driver of a potential collision via a vibrating pulse in the left or right side of the seat.

New powertrains

The next-gen Silverado and Sierra will be offered with three choices from GM's new family of EcoTec3 engines: a 5.3-liter V-8, which is expected to be the volume engine; a 6.2-liter V-8; and a 4.3-liter, naturally aspirated V-6.

A GM spokesman said that official federal mileage ratings won't be assigned until early next year. But GM is confident that each of the three engines will get better fuel economy than its predecessor.

The 2013 pickups offer a 4.3-liter V-6 that gets 15 mpg in city driving and 20 on the highway in a regular cab truck; a 4.8-liter V-8 that gets 14 mpg city/19 highway in a regular cab; a 5.3-liter V-8 that gets 15 mpg city/21 highway in an extended cab; and a 6.2-liter V-8 rated 13mpg city/18 highway in an extended cab. Fuel economy ratings are based on two-wheel-drive mode.

The 2014 pickups will be mated to six-speed transmissions. Sources say GM plans to eventually offer an eight-speed transmission, but it likely won't be added for at least a year.

GM powertrain engineers spent five years developing the engine family for the fifth-generation small block. A version also will be in the redesigned Corvette due out next year. The overhead-valve pushrod engine will be built in Tonawanda, N.Y.

The addition of direct injection was a key to an improved combustion system that allows the engine to consume fuel more efficiently. The system sprays fuel directly into the cylinders, which more precisely controls the fuel-air mixture. The new engine block is aluminum, which also reduces weight.

Cylinder deactivation, which shuts down four of the eight cylinders under light loads, will come standard on all models. Today, it's only offered on higher trim levels. GM engineers say the new engines will allow the vehicle to operate for longer periods in four-cylinder mode, which should wring out further fuel savings.

'Benchmark' interior

GM vastly improved the pickups' interiors, which are relatively spartan on current models, and says the new styling "sets a benchmark for full-sized trucks." Higher trim levels have plenty of soft-touch material and aluminum trim.

GM used more durable, "dual density" foam in the front seats for better comfort. Lower trim levels will come with cloth seats that use new "high-wear" material that resists staining.

The Silverado and Sierra will come with an optional 8-inch color touch screen displaying GM's infotainment offerings. Big knobs and interfaces were designed for ease of use, even for drivers wearing work gloves. A 4-inch information screen in the instrument panel, also optional, displays vehicle and infotainment data.

GM improved rear-seat access on both extended and crew cabs. The rear doors on the crew cabs are larger, while the doors on extended cab models now hinge at the front, allowing rear-seat passengers to enter and exit without opening the front door.

GM also addressed a problem spot on the current truck -- tight rear legroom compared with rival pickups -- by pulling forward the B-pillars slightly and narrowing the backs of the front seats, changes that added about 2 inches of rear legroom.